Regulation of Apoptosis in the Testis

Abstract

It has become clear that germ cell death in the testis, inducible by a variety of rather diverse factors and circumstances, invariably proceeds via a process resembling that of active cell death, called apoptosis as described for other cell types (for review, see 1). Apoptosis may take place following several pathways, probably dependent on the kind of apoptotic stimulus the cells get. The regulation of apoptosis has appeared to be of increasing complexity. Apoptosis can be divided into phases (2), with the various apoptosis regulators acting during different phases of the apoptotic pathway. In the first phase, the cell becomes affected by an apoptotic stimulus. For germ cells, many factors have been shown to directly or indirectly act as an apoptotic stimulus, such as temperature, hormone levels, and xenobiotic agents like radiation and cytostatic drugs (1). In the second phase, the cell detects the apoptotic stimulus, whereafter, in phase three, the cell responds. Finally, at phase four, the cell completely degrades. Proteins involved in apoptosis regulation in each of these phases were shown to be expressed in the testis, leading to an initial understanding of which apoptotic pathways are present in germ cells. As the factors involved in the first phase of apoptosis induction have already been described in this volume (1), only the factors that regulate other phases of apoptosis will be described in this chapter, with the emphasis on those already known to be expressed in the testis (Table 19.1).